1. Field of the Invention
The present invention relates to an apparatus for detecting the amount of deviation of the stop position of a mobile body with, for example, a working machine mounted thereon, from a predetermined stop position, and an apparatus for position correction for the working machine based on the amount of deviation of the stop position.
2. Description of the Prior Art
In manufacturing processes or the like, robots mounted on unmanned carriages are typically used, each of which is designed in such a manner that as an unmanned carriage (mobile body) with a robot (working machine) mounted thereon stops at a predetermined work position, the robot performs a predetermined work at the stop position. According to this type of machine, the robot works in accordance with teaching data, which was previously acquired with the unmanned carriage stopped at the work position. However, generally, the position precision of the unmanned carriage is low and it is difficult to precisely stop the unmanned carriage at the stop position at which the teaching data was acquired. The relative position between the actual stop position of the unmanned carriage and an intended work position varies frequently. This requires correction to reflect an error in the stop position of the unmanned carriage in the teaching data. One way of correcting the position of such a robot mounted on an unmanned carriage is disclosed in, for example, Japanese Patent Publication No. 9151 of 1996 (hereinafter called prior art) An arm-equipped unmanned carriage A0 according to this prior art is constructed as shown in FIG. 27. An unmanned carriage 131 has an arm 132 so constructed as to be able to rotate horizontally and move to and fro as well as up and down. A pickup sensor 133 and a hand 134 are attached to the front end of the arm 132. Furthermore, a work 136 which is to be grabbed and moved by the hand 134 of the arm 132 is placed on a workbench 135 at a predetermined position. A mark 137 consisting of two points 137a and 137b is provided on the upper face of the workbench 135. The unmanned carriage 131 runs among a plurality of workbenches 135, and stops at a predetermined position in front of each workbench 135 and carries out predetermined work on the work 136 using the arm 132 in accordance with the previously given teaching data.
A description will be given of a means that the arm-installed unmanned carriage A0 with the above structure accurately implements the operation with the arm 132, regardless of an error or deviation of the stop position in front of each workbench 135 from the original stop position where the teaching data was acquired.
First, at the time of teaching the operations to the arm 132 prior to the actual work, a normal intended work position and a point for picking up the mark 137 are taught. Specifically, the pickup sensor 133 is moved directly above the mark 137 and this position is taught, then the mark 137 is picked up by the pickup sensor 133 and the obtained picked image is subjected to predetermined image processing to acquire the coordinate position (called teaching-time coordinate position) of the marks 137a and 137b on the picked image, and the coordinate position is stored in memory.
Next, after the unmanned carriage 131 stops in front of the workbench 135 to work, first, the arm 132 moves the pickup sensor 133 above the mark 137 to pick up the mark 137 according to the taught procedures, performs predetermined image processing on the acquired picked image to obtain the coordinate position (called work-time coordinate position) of the marks 137a and 137b on the picked image. Because the positioning precision of the unmanned carriage 131 is generally poor, the teaching-time coordinate position acquired at the time of teaching often does not match with the work-time coordinate position. In this case, a conversion equation is obtained based on the amount of position deviation between the teaching-time coordinate position and the work-time coordinate position and the teaching data (which indicates the intended work position) of the arm 132 is corrected according to the equation.
The above-described process allows the arm 132 to accurately work irrespective of the amount of deviation of the stop position of the unmanned carriage 131.
The means of the prior art however requires that after the unmanned carriage 131 stops in front of each workbench 135 and before it starts the actual work with the arm 132, the arm 132 should be operated to conduct the following processes.
1 Manipulate the arm 132 to move the pickup sensor 133 over the mark 137.
2 Pick up the mark 137 by means of the pickup sensor 133 and perform image processing.
3 Correct the teaching data.
These processes involve the operation of the arm 132 and thus take time, during which the arm 132 cannot proceed to the next work, and are thus critical factors to increase the working time of the overall system.
As an arm has many parts which may cause control errors, such as the link portions and driving portions, it is ideal from the viewpoint of precision to correct an error at the front end of the arm, which is closest to the point of action, in order to operate the arm precisely with respect to a work. Conventionally, the above-described correction has been executed along this idea. The recent technical improvements however can reduce the control errors to such a level that error correction at the arm's free end is not necessarily required.